Other generic kind of procedures and systems of different makes are known.
Therefore it is known that the deflection of a—small—laser beam which is sent through a heated zone of a liquid can be used to measure the velocity of the liquid. The heated zone of the liquid is warmed up by a different device than the laser.
Alternatively, it is known how to measure the flow velocity of a liquid if necessary by means of a down-stream array of optical detectors and an optically produced heating point during the running time of a temporarily heated area from the heating point to the measuring point.
Disadvantageously, in this case two different workspace locations as well as working equipments are needed: the heating system and the heating detection system. The invention has therefore the aim to develop an improved procedure as well as a developed apparatus to define the velocity of a flowing liquid and to avoid the disadvantages mentioned before.